One long term objective is to design glassy dental polymers which take up a limited amount of water in a manner which can be predicted from chemical structure. Another long term objective is to predict how uptake of water will affect mechanical properties. Aim 1 is to determine how dynamic mechanical properties of composite tooth restorative materials are affected by saturation with water and with artifical saliva. This aim includes determination of the glass transition temperature, Tg, above which a polymer loses rigidity. Specimens are subjected to a sinusoidal force and scanned over a range of temperatures. Aim 2 is to determine how the amount of water taken up affects mechanical propteries such as hardness, elastic modulus, and tensile strength. Water uptake will be varied by control of relative humidity. The hypothesis is that the effect of water is influenced by the extent to which it is present in molecular clusters. This hypothesis will be tested by analysis of volumetric changes accompanying water sorption, of sorption isotherms, and of 13C rotating-frame relaxation times. Aim 3 is to complete uptake of water by methacrylate monomers with uptake by their corresponding polymers. Water sorption by monomers will be ranked by Karl Fischer analysis: Polymers will be ranked gravimetrically. The hypothesis is that relative uptake of water by the polymers is determined primarily by the hydrophilicity of constituent atomic groups from the monomers. Aim 4 is to determine how the diffusion and sorption of water in polydimethacrylates depends on secondary factors such as crosslink density and Tg. Crosslink density will be estimated from measurements of elastic modulus at temperatures above Tg. The hypotheses are that water sorption increases with increase in crosslink density and temperature. Aim 5 is to study the diffusion and sorption of water by polymers made from mixtures of polymethacrylate powder, liquid monomers, and plasticizers. One objective is to study the influence of microphase separation. Another objective is to relate this work to similar studies of soft reliners, recovered from patients, afte failure in service.